a. Field of Invention
This invention relates to methods and compositions for improving anesthesia.
B. Prior Art
Anesthesia is generally looked upon as being composed of analgesia, unconciousness, depression or abolition of reflex activity and muscle relaxation. Neuroleptanalgesia (NLA), produced by the administration of a potent analgesic and a potent neuroleptic, is accepted as a fully adequate replacement for orthodox general anesthesia. Unlike orthodox general anesthesia, with the NLA method each of the elements -- analgesia, neurolepsy and muscle relaxation -- may be controlled separately and adapted to the needs of the individual patient, especially as far as degree and duration of activity are concerned. The emphasis in NLA is on the analgesic state provided by the narcotic analgesic and potentiated and improved by the psychic indifference and lack of initiative induced by the neuroleptic. When used in a suitable combination, these two drugs -- the neuroleptic and the analgesic -- can produce what has been called the neuroleptanalgesic state. In such a state, patients can undergo most surgical procedures. Since a minimum of noxious substances are administered, these patients emerge from such procedures with no significant metabolic derangement and with a reduced risk of serious complications.
General anesthesia, as obtained with the inhalation anesthetics or intravenous barbiturates, influences cell metabolism extensively, resulting in metabolic acidosis. Oxidative processes are depressed while intermediate metabolic reactions are more pronounced. On the other hand, the very slight degree of central depression and metabolic alteration, together with the low toxicity and stable circulation, makes the NLA procedure nearly ideal for poor risk and geriatric patients. The psychic indifference obtained with the NLA combination puts considerably less stress on the patient than complete unconsciousness. Since the NLA procedure is specially applicable to the elderly and poor risk patient, it would seem reasonable to extend this application to the normal healthy patient.
NLA has been called "balanced anesthesia" and can be defined as the use of drugs with highly specific action to achieve certain results necessary in order that a patient will tolerate a surgical or diagnostic procedure.
An important application of NLA is its use as a supplement to light general anesthesia; e.g., nitrous oxide, halothane. In this connection, the term "neuroleptanesthesia" was proposed by F. F. Foldes, et al., Anesth. Analg., 45, 642(1966) to characterize the state of patients receiving a neuroleptic, a narcotic analgesic and a general anesthetic, so that they become analgetic, sedated and anesthetized. It was further suggested by the investigators that the term neuroleptanalgesia be restricted to patients given neuroleptic and narcotic analgesic agents who became analgetic, sedated and amnesic -- but are capable of obeying commands during surgery.
Moreover, it is now clear that in certain surgical and diagnostic procedures the NLA combination alone provides as satisfactory anesthesia as any other method and is considered by many to be superior.
On the other hand, only a few methods and preparations are available for NLA, see for example, U.S. Pat. No. 3,141,823, issued July 21, 1964 and U.S. Pat. No. 3,662,073 issued May 9, 1972, and only one pharmaceutical composition, droperidol-fentanyl, the subject matter of the former patent, is used to any degree in the field of anesthesia. Furthermore, not all combinations of known neuroleptic agents and analgesic agents are capable of producing neuroleptanalgesia. Accordingly, the search for improved methods and compositions for NLA goes on.
In this respect the present disclosure describes a novel method and compositions for effecting anesthesia. The method and compositions are applicable to NLA and have the attribute of improved safety features such as significantly less disturbances of the cardiovascular system.